This is not something we do on a regular basis as it's more of a traditional English dish. But we had some French clients request it and we rose to the occasion. Beef wellington it shall be!
It's actually a lot easier to make than it seems! Honestly - the trickiest part is timing it well so that the crust is nice and golden and crispy, and the beef tenderloin is rare. Having usually made smaller versions of less than 1 kilo I wasn't exactly sure of the cooking time on a 2 kilo one - especially as it was quite thick. The pastry really only takes about 35 minutes to brown, as does cooking a 1 - 2 kilo rare beef tenderloin give or take 5-6 minutes. We cooked this 2 kilo filet for 36 minutes and it came out perfectly rare, the crust perfectly crunchy. This served 12 persons generously.
I did not bother with wrapping it in plastic and putting it back in the fridge 2 x as a lot of recipes call for - this can all be done in one go with the same results. I prefer to get my beef to room temperature first which ensures more even cooking. The pastry does need to be re chilled after assembly- with the beef but it acts as a blanket so hopefully the beef remains a temperature ambiant.. Once it's come to room temp sear the beef on all sides on high heat browning well. Take out of the pan and coat the beef in Dijon mustard on all sides and let rest. Prepare the druxelle - finely chop up 250 gm of button mushrooms- I used the dark variety which are called Champignons de Paris in France. Best to mince them finely in the food processor - you don't want a paste but a tiny mince. Then Sautée them in a bit of butter using the beef pan, adding 2 cloves of minced garlic towards the end, allow the water to cook off. I turn them out onto paper towels afterwards to dry a bit further. As you don't want them to contribute to making a soggy en croute. The goal is that it to be somewhat dry. Set aside or in the fridge to cool. I used organic store bought all butter puff pastry for the en croute, but you could certainly make your own - which would preclude any mention of easy in this recipe title! Once the druxelle is cooled down completely take the puff paste out of the fridge and start assembling - you don't have to do the lattice like decoration which is made by simply slicing holes in a second entire sheet of puff pastry but it's a good idea to use 2 sheets if your making a beef Wellington of this size as it will take slightly longer to cook the pastry than if you had 1 sheet. You could also just make ribbon strips with the excess and place these on top or any form you want really when making a smaller piece of beef.
Assemble as quickly as possible as you want the pastry to stay cold - this will help it be crispier.
Place a sufficiently large piece of plastic wrap down on the counter to wrap the beef - add the pastry first, then the prosciutto ham, the druxelle in a thin layer, then the beef. Wrap the pastry all around the beef and press it together. Wrap the entire log in plastic wrap and place back in the fridge for 10 minutes or so.
Preheat the oven to 220 c or 400 f. Remove the plastic from your beef Wellington and cook in middle center of the oven for 38minutes. Just after putting it into the oven turn down the oven temperature to 180 c /350f. The pastry should be nice and brown.
Let sit outside the oven before cutting for at least 7-10 minutes. This ensures that the juices got back into the beef and don't run out into the pasty crust.